The present invention relates to a digital control unit for controlling a sound-slide projector and more particularly to a digital control unit for controlling a sound projector which permits the random selection of slides to be projected.
In the prior art, there are many sound-slide projectors of the type which include a movable audio disk having a transparency mounted coaxial therewith in which a plurality of different slides are mounted in a tray movable parallel to the optical projection axis. A slide changing mechanism driven by a fly wheel, a slide projection system and a sound transmission unit of the type referred to are shown in U.S. Pat. No. 3,732,000 to Annette et al.
In prior art projectors of this type such as that shown by the Annette et al. patent, the presentation of sound - slides carried in a slide tray occurs as follows. A tray carrying a pre-determined number of slides is inserted into a channel from the rear of the projector. To align the first slide with an insertion slot of the projector assembly, a handle on the slide changing mechanism must be operated. The slide tray can then be advanced until the first slide is correctly aligned with a slide insertion push rod at the edge of a slot in the slide tray and with the insertion slot of the projector. The handle is then manually operated so that the slide insertion push rod pushes the first slide from the slide tray into projection position.
At this point a pressure roller actuated control arm with a slide return guide rod is activated so that a spring presses a pressure roller against a drive roller and against the audio disk on the slide. The audio disk is then rotated about its own axis while a pick-up engages the disk for recording or playback. The drive roller and pressure roller rotate the audio disk with a constant angular velocity. When the transmitter or pickup has reached the end of the sound track, electrical contacts are closed to energize a solenoid. This solenoid causes a roller to rotate a gear wheel or pinion. A cylindrical projection or pin on the pinion then initiates the return of the slide to the slide tray, by way of the control arm and a slide-return guide-rod connected to the slide insertion pushrod.
At the start of the slide return process, the transmitter pickup and the pressure roller are caused to disengage from the audio disc so that rotation of the audio disc stops.
As the pinion continues to rotate the slide-return guide-rod guides the slide completely back into the proper compartment of the slide tray, which is then advanced one position by a gear, so that the next compartment is aligned with the insertion slot.
Rotation of the pinion finally causes insertion of the slide in the new compartment into projection position by the slide-insertion pushrod. As soon as this position is reached, driving of the pinion is interrupted, and the pressure roller, the drive roller and the transmitter pickup are engaged with the audio disc. Then the transparency carried in the sound slide is projected, and simultaneously, information can be recorded in the audio disc or played back from it.
Each slide can be transported from the slide tray to projection position and then returned to the slide tray in the aforementioned manner.
It will be seen that such projectors operate only with a slide tray which moves forwardly step-by-step, or one slide at a time, and they only permit exhibition of the slides in a fixed sequence. The order of presentation is pre-determined by the storing or placement of the slides in the slide tray, so that a change in the sequence is not possible.